netdev - Re: [PATCH net] net/smc: Stop the CLC flow if no link to map buffers on

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Message-ID: <2f6ba289-050a-f77b-3cd2-694317f070bb@linux.ibm.com>
Date:   Thu, 22 Sep 2022 15:07:38 +0200
From:   Wenjia Zhang <wenjia@...ux.ibm.com>
To:     Wen Gu <guwen@...ux.alibaba.com>, kgraul@...ux.ibm.com
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: Stop the CLC flow if no link to map buffers
 on



On 22.09.22 10:29, Wen Gu wrote:
> 
> 
> On 2022/9/20 14:43, Wen Gu wrote:
> 
>> There might be a potential race between SMC-R buffer map and
>> link group termination.
>>
>> smc_smcr_terminate_all()     | smc_connect_rdma()
>> --------------------------------------------------------------
>>                               | smc_conn_create()
>> for links in smcibdev        |
>>          schedule links down  |
>>                               | smc_buf_create()
>>                               |  \- smcr_buf_map_usable_links()
>>                               |      \- no usable links found,
>>                               |         (rmb->mr = NULL)
>>                               |
>>                               | smc_clc_send_confirm()
>>                               |  \- access conn->rmb_desc->mr[]->rkey
>>                               |     (panic)
>>
>> During reboot and IB device module remove, all links will be set
>> down and no usable links remain in link groups. In such situation
>> smcr_buf_map_usable_links() should return an error and stop the
>> CLC flow accessing to uninitialized mr.
>>
>> Fixes: b9247544c1bc ("net/smc: convert static link ID instances to 
>> support multiple links")
>> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>> ---
>>   net/smc/smc_core.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
>> index ebf56cd..df89c2e 100644
>> --- a/net/smc/smc_core.c
>> +++ b/net/smc/smc_core.c
>> @@ -2239,7 +2239,7 @@ static struct smc_buf_desc 
>> *smcr_new_buf_create(struct smc_link_group *lgr,
>>   static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
>>                        struct smc_buf_desc *buf_desc, bool is_rmb)
>>   {
>> -    int i, rc = 0;
>> +    int i, rc = 0, cnt = 0;
>>       /* protect against parallel link reconfiguration */
>>       mutex_lock(&lgr->llc_conf_mutex);
>> @@ -2252,9 +2252,12 @@ static int smcr_buf_map_usable_links(struct 
>> smc_link_group *lgr,
>>               rc = -ENOMEM;
>>               goto out;
>>           }
>> +        cnt++;
>>       }
>>   out:
>>       mutex_unlock(&lgr->llc_conf_mutex);
>> +    if (!rc && !cnt)
>> +        rc = -EINVAL;
>>       return rc;
>>   }
> 
> Any comments or reviews are welcome and appreciated.
> 
> Thanks,
> Wen Gu

Sorry for the late answer!
Good catch! Thank you!

Acked-by: Wenjia Zhang <wenjia@...ux.ibm.com>